EP3361929B1 - Device for testing the visual behavior of a person, and method for determining at least one optical design parameter of an ophthalmic lens using such a device - Google Patents

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES

The present invention relates generally to a test device for determining the visual behavior of an individual.

It also relates to a method for determining at least one optical design parameter of an ophthalmic lens using such a device.

TECHNOLOGICAL BACKGROUND

The ever more precise personalization of the ophthalmic lenses of a frame intended to equip an individual to correct his vision requires an increased knowledge of the visual behavior of the individual under vision conditions which are natural and representative of the actual use of said ophthalmic lenses. .

The determination of parameters of the visual behavior of the individual then makes it possible to improve the optical design of the ophthalmic lenses which will be mounted in the frame.

In particular, during the optical design of progressive ophthalmic lenses, it is particularly important to have optical design data that is relevant to account for the use of these lenses in near vision and the posture taken by the individual. , especially in a reading situation.

However, the measurements currently carried out by the optician on the individual are most often constrained, in particular due to the fact that the individual does not wear a correction or that the measuring devices or visual test devices used place the individual in a unnatural posture, especially in near vision.

It is the same when the individual wears a correction, which, moreover, can no longer be adapted to his refraction. In this case, the measurements are falsified because the optical power impacts the posture due to the prismatic effect of the correction.

In addition, it is difficult to put the individual in a reading situation in a natural posture, without the latter being equipped with his visual correction equipment, individuals suffering from myopia tend to reduce the reading distance, while those with presbyopia tend to increase this distance.

Conversely, a measurement made by asking the individual to perform a visual task other than reading departs from natural conditions and therefore from a measurement representative of the use of a progressive lens on a daily basis.

The visual test devices are therefore imprecise and the optical design parameters determined by the optician are therefore not always representative of the visual behavior of the individual under natural conditions.

As a result, the optical design of progressive lenses is not optimal so that adaptation of progressive ophthalmic lenses to the wearer can be difficult.

The document WO 2008/139137 describes a device for testing the visual behavior of an individual according to the preamble of claim 1.

OBJECT OF THE INVENTION

In order to remedy the aforementioned drawback of the state of the art, the present invention proposes a device for testing the visual behavior of an individual making it possible to determine the visual behavior of an individual in a simple and precise manner.

• un afficheur actif adapté à afficher au moins une cible visuellement prépondérante en une pluralité de positions variables au cours du temps et alignées selon au moins une ligne ou une colonne, et
• une unité de commande de l'afficheur, programmée pour que les positions d'affichage successives de la cible suivent, au cours du temps, un protocole de suivi visuel.

More particularly, according to the invention there is proposed a device for testing the visual behavior of an individual comprising:

• an active display adapted to display at least one visually preponderant target in a plurality of positions varying over time and aligned along at least one row or one column, and
• a display control unit, programmed so that the successive display positions of the target follow, over time, a visual monitoring protocol.

Thus, thanks to the device according to the invention, it is possible to test the visual behavior of the individual in a reading situation under natural conditions. Said target can be watched by any individual, adult or child, able to read or not, and independently of the language spoken by the individual. In addition, the target can be followed by gaze even in the absence of visual correction worn by the individual.

In particular, it is possible to provide that all the display positions successive are such that the target is in the visual field of the individual. In other words, the individual can follow the target throughout the visual test.

Thus, there is no risk that a target, visually preponderant or not, will not be detected by the test device.

On the contrary, the test device is designed to require the individual to look in very specific directions of his visual field, and in no way outside it, at the risk of introducing risks of measurement error. .

Thanks to the device according to the invention, a precise visual behavior parameter of the individual can be determined.

According to a particularly advantageous characteristic of the invention, said positions of the target are aligned along at least two rows or two substantially parallel columns.

Again advantageously, said plurality of positions comprises, on each row or column, at least three aligned positions of said target.

• l'unité de commande impose, dans chaque position dudit protocole de suivi visuel, que la cible s'affiche pendant une durée prédéterminée ;
• ladite durée prédéterminée est comprise entre 50 millisecondes et 1 seconde ;
• ladite cible est fixe pendant ladite durée prédéterminée ;
• l'unité de commande impose un délai prédéterminé entre les affichages de la cible dans deux positions successives du protocole de suivi visuel ;
• ledit délai prédéterminé varie au cours du protocole de suivi visuel ;
• ladite cible est invisible pendant ledit délai prédéterminé ;
• ladite cible est visible pendant ledit délai prédéterminé et se déplace entre les deux positions successives correspondantes du protocole de suivi visuel, de l'une à l'autre ;
• ladite unité de commande impose que deux positions successives du protocole de suivi visuel sont séparées d'une distance inférieure à 10 centimètres ;
• ladite unité de commande impose que deux positions successives du protocole de suivi visuel sont séparées d'une distance variant le long du protocole de suivi visuel ;
• ladite unité de commande mémorise un sens de parcours vertical et horizontal privilégié du protocole de suivi visuel ;
• l'affichage de ladite cible dans deux positions successives du protocole de suivi visuel suit ledit sens de parcours privilégié au moins six fois sur dix ;
• lesdites lignes sensiblement parallèles le long desquelles sont alignées les positions prédéterminées de la cible s'étendant sensiblement horizontalement, le sens de parcours du protocole de suivi visuel est identique pour toutes les lignes prises successivement de la plus haute à la plus basse, de droite à gauche ou de gauche à droite ;
• lesdites lignes sensiblement parallèles le long desquelles sont alignées les positions prédéterminées de la cible s'étendant sensiblement verticalement, le sens de parcours du protocole de suivi visuel est identique, de haut en bas ou de bas en haut, pour toutes les lignes prises successivement de gauche à droite ou de droite à gauche ;
• l'unité de commande est programmée pour permettre la sélection dudit protocole de suivi visuel parmi une pluralité de protocoles de suivi visuel enregistrée dans une base de données locale ou distante, dans laquelle un sens de parcours est enregistré en association avec le protocole de suivi visuel auquel il correspond ;
• le protocole de suivi visuel suit un trajet de lecture conforme à celui défini par un système d'écriture donné, de manière à reproduire le déplacement du regard de l'individu pendant la lecture conformément au système d'écriture.

Other non-limiting and advantageous characteristics of the method according to the invention, taken individually or according to any technically possible combination, are as follows:

• the control unit requires, in each position of said visual tracking protocol, that the target is displayed for a predetermined time;
• said predetermined duration is between 50 milliseconds and 1 second;
• said target is fixed for said predetermined time;
• the control unit imposes a predetermined delay between displays of the target in two successive positions of the visual tracking protocol;
• said predetermined time varies during the visual monitoring protocol;
• said target is invisible for said predetermined time;
• said target is visible for said predetermined time and moves between the two corresponding successive positions of the visual tracking protocol, from one to the other;
• said control unit requires that two successive positions of the visual tracking protocol are separated by a distance of less than 10 centimeters;
• said control unit requires that two successive positions of the visual tracking protocol are separated by a distance varying along the protocol visual monitoring;
• said control unit memorizes a preferred vertical and horizontal travel direction of the visual tracking protocol;
• the display of said target in two successive positions of the visual tracking protocol follows said preferred direction of travel at least six times out of ten;
• said substantially parallel lines along which are aligned the predetermined positions of the target extending substantially horizontally, the direction of travel of the visual tracking protocol is identical for all the lines taken successively from highest to lowest, from right to left or left to right;
• said substantially parallel lines along which are aligned the predetermined positions of the target extending substantially vertically, the direction of travel of the visual tracking protocol is identical, from top to bottom or from bottom to top, for all the lines taken successively from left to right or right to left;
• the control unit is programmed to allow selection of said visual tracking protocol from among a plurality of visual tracking protocols stored in a local or remote database, in which a direction of travel is recorded in association with the visual tracking protocol to which it corresponds;
• the visual tracking protocol follows a reading path conforming to that defined by a given writing system, so as to reproduce the movement of the gaze of the individual during reading in accordance with the writing system.

The invention also proposes a method for determining at least one optical design parameter of an ophthalmic lens intended to equip a frame chosen by an individual, as a function of the visual behavior of the latter.

1. a) on demande à l'individu d'effectuer une tâche visuelle dans laquelle il regarde la cible affichée par ledit afficheur du dispositif d'affichage, les positions de ladite cible étant prédéterminées dans un référentiel lié à un appareil de capture d'image,
2. b) on capture, au moyen dudit appareil de capture d'image, des images de la tête de l'individu regardant ladite cible, chaque image correspondant à une position prédéterminée de ladite cible,
3. c) on détermine, à partir d'une partie au moins des images de la tête de l'individu, des positions de la tête de l'individu dans un référentiel lié audit appareil de capture d'image ou des directions de regard de l'individu dans un référentiel lié à la tête de l'individu, chaque position de la tête ou direction de regard de l'individu étant associée à la position de ladite cible pour laquelle l'image correspondante de la tête de l'individu a été capturée,
4. d) on déduit ledit paramètre de conception optique recherché à partir desdites positions de tête ou direction de regard de l'individu.

According to the invention, this method uses the aforementioned test device and comprises the following steps:

1. a) the individual is asked to perform a visual task in which he looks at the target displayed by said display of the display device, the positions of said target being predetermined in a frame of reference linked to an image capture device,
2. b) capturing, by means of said image capture device, images of the head of the individual looking at said target, each image corresponding to a predetermined position of said target,
3. c) determining, from at least part of the images of the individual's head, the positions of the individual's head in a frame of reference linked to said image capture device or the gaze directions of the individual. 'individual in a frame of reference linked to the head of the individual, each position of the head or direction of gaze of the individual being associated with the position of said target for which the corresponding image of the head of the individual has been captured,
4. d) said desired optical design parameter is deduced from said head positions or direction of gaze of the individual.

The method according to the invention makes it possible to determine an optical design parameter which is representative of the visual behavior of the individual.

The determination of the optical design parameter using this method thus allows better adaptation of the vision zones of the ophthalmic lens, as a function of the characteristics of the individual.

According to a particularly advantageous characteristic of the invention, prior to step d), the positions of said target are reexpressed from said determined positions of the head or from the viewing directions of the individual, the positions of said target in a frame of reference linked to the head of the individual, and in step d), said desired optical design parameter is deduced from said positions of the target in the frame of reference linked to the head of the individual.

DETAILED DESCRIPTION OF AN EXAMPLE OF AN IMPLEMENTATION

The description which will follow with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be implemented.

• la figure 1 est une vue schématique d'un individu tenant dans ses mains un dispositif de test conforme à l'invention ;
• la figure 2 est une vue de face du dispositif de test de la figure 1 ;
• la figure 3 est une vue schématique rassemblant différents protocoles de suivi visuel utilisés dans le dispositif de la figure 1 ;
• la figure 4 représente un diagramme d'une méthode de détermination d'un paramètre de conception optique utilisant le dispositif de la figure 1 ;
• la figure 5 est une vue schématique de la tête de l'individu ;
• la figure 6 représente un repère lié à la tête de l'individu ;
• les figures 7 à 11 représentent le dispositif de test de la figure 1 lors de différentes étapes d'une phase de réglage de la méthode de l'invention ;
• la figure 12 illustre un repère lié au dispositif de test de la figure 1 ;
• la figure 13 représente le dispositif de test de la figure 1 lors d'une étape d'une phase d'entraînement de la méthode de l'invention ;
• les figures 14 et 15 représentent le dispositif de test lors d'une étape de vérification d'une phase de mesure de la méthode de l'invention ;
• la figure 16 représente l'afficheur du dispositif de test avec des cibles affichées et un repère lié à la tête de l'individu regardant la cible dans une position finale du protocole ;
• les figures 17 et 18 représentent des exemples de positions mesurées de la cible dans le référentiel lié à la tête de l'individu au cours du protocole de lecture.

In the accompanying drawings:

• the figure 1 is a schematic view of an individual holding in his hands a test device according to the invention;
• the figure 2 is a front view of the device for testing figure 1 ;
• the figure 3 is a schematic view bringing together different visual monitoring protocols used in the device of the figure 1 ;
• the figure 4 represents a diagram of a method of determining an optical design parameter using the device of the figure 1 ;
• the figure 5 is a schematic view of the individual's head;
• the figure 6 represents a mark linked to the head of the individual;
• the figures 7 to 11 represent the test device of the figure 1 during different steps of a phase of adjustment of the method of the invention;
• the figure 12 illustrates a marker linked to the test device of the figure 1 ;
• the figure 13 represents the test device of the figure 1 during a step of a training phase of the method of the invention;
• the figures 14 and 15 represent the test device during a verification step of a measurement phase of the method of the invention;
• the figure 16 shows the display of the test device with targets displayed and a mark linked to the head of the individual looking at the target in a final position of the protocol;
• the figures 17 and 18 represent examples of measured positions of the target in the frame of reference linked to the head of the individual during the reading protocol.

As a preamble, it will be noted that the identical or similar elements of the various embodiments shown in the various figures will be referenced by the same reference signs and will not be described each time.

It will also be noted that in the description which follows, the terms “high” (or “upper”) and “low” (or “lower”) will be used in relation to the individual using the test device, the top designating the person using the test device. side facing the individual's head and downward designating the side facing the individual's feet.

Likewise, the term "front" will denote the side facing the individual, the term "rear" denoting the side opposite to the front side.

On the figure 1 , there is shown an individual 1 whose visual behavior is to be tested.

To this end, the individual 1 holds in his hands 2 a test device 10 in accordance with the invention intended to determine this visual behavior under given conditions.

More particularly here, it is desired to use the test device 10 to generally analyze the near vision of the individual 1, and in particular the visual behavior that he adopts when he is in a reading situation.

We will consider that the near vision corresponds to an observation distance DO (see figure 1 ) between eye 3 of individual 1 and test device 10 less than 70 centimeters (cm).

In other embodiments, the intermediate vision (OD between 70 cm and 4 meters) or far vision (OD greater than 4 m) can be tested using the test device according to the invention.

• un afficheur 11 actif qui affiche une cible 20 visuellement prépondérante en une pluralité de positions 30 variables au cours du temps et alignées selon au moins une ligne ou une colonne, et
• une unité de commande (non représentée) de l'afficheur 11, programmée pour que les positions 30 d'affichage successives de la cible 20 suivent, au cours du temps, un protocole de suivi visuel, dans lequel toutes les positions d'affichage successives sont telles que la cible est dans le champ visuel de l'individu.

According to the invention, the test device 10 comprises (see figure 2 ):

• an active display 11 which displays a visually preponderant target 20 in a plurality of positions 30 varying over time and aligned along at least one row or one column, and
• a control unit (not shown) of the display 11, programmed so that the successive display positions of the target 20 follow, over time, a visual tracking protocol, in which all the successive display positions are such that the target is within the visual field of the individual.

The display 11 of the test device can display, at each instant of the visual test, a single target or else several targets simultaneously, each target being in the visual field of the individual. In both cases, the visually preponderant target is that which is adapted to catch the eye of the individual and that the individual will follow during the visual test.

If it was not in the visual field of the individual, he could not detect it.

When several targets are displayed by the display 11 in the visual field of the individual, the visually preponderant target can be, for example, a brighter or more contrasted target, of color or shape (round, square, star,. ..) different, or smaller or larger in size than the others, or even a target that flashes while the others are not. The different targets displayed by the display can also include a set of indicators or else form a grid of gray dots.

In the embodiments where the display only displays a single target, the latter can take a plurality of positions on the display 11, insofar as the positions taken remain in the visual field of the individual. These positions are "variable" in that the target moves sequentially from one position to another during the visual test. Note, however, that the sequence of positions taken successively by the target in these embodiments can comprise two identical positions. In other words, it is possible that during the visual test the target passes through a position already taken previously.

In the embodiments where the display displays several targets, one of which is visually preponderant, the display positions of the targets can be variable over time, within the visual field of the individual, but in total. In this case, the visually predominant target is that which moves according to a sequence of positions in the visual field of the individual so as to impose on the individual 1 a succession of particular gaze directions.

In the present description, the term “ visual monitoring protocol ” will therefore be understood to mean the display sequence of the visually dominant target 20 during the visual test carried out by the individual 1, these successive display positions being such as the target 20. is in the visual field of the individual 1.

In other words, this visual monitoring protocol corresponds to the succession, over time, of the positions taken by the visually predominant target. Thanks to this, a protocol is imposed on the individual who looks successively in a plurality of particular desired directions which are each associated with a particular position taken by the target. In this way, if the positions of this target are known, it is then possible, under certain conditions, to go back to the information concerning the direction of gaze of the individual during the visual test.

As shown on the figure 2 , the test device 10 is here in the form of a digital tablet. This digital tablet comprises a screen which constitutes the display 11 of the test device 10. It also comprises a housing 12 surrounding the screen and a front camera 13 aimed at the individual 1. The control unit of the device 10 corresponds, as far as to it, to the display controller of the tablet screen which is housed inside the housing 12.

The target 20 here comprises a luminous disc which is displayed on the screen of the tablet, the size of the target being sufficient for it to be visible by the individual 1 under the conditions of the visual test. Here, under reading conditions and in near vision (OD <70 cm), the target 20 has a characteristic size (eg diameter) greater than 5 millimeters.

Advantageously, the characteristic size of the target 20 is determined such that it can be seen with acuity greater than 0.1 tenth at 70 cm.

As a variant, the target can comprise a geometric pattern, regular or not. It is preferably any pattern, excluding a sign used by any writing system understandable by the individual. In particular, the visually dominant target is meaningless for the individual. For example, the target is not a word intelligible to the individual.

We will now describe, with reference to the figure 4 , different types of visual monitoring protocols which are implemented by the test device 10 according to the invention and which are intended here to simulate the reading of a text by the individual 1.

Advantageously, the display of the target according to the visual monitoring protocols implemented by the test device 10 constitutes a visual stimulus for the individual 1, intended to make him move his eyes by monitoring this target 20 according to the same pattern that individual 1 would adopt if he were actually reading a text.

In other words, the display of the visually preponderant target on the display is controlled such that when the individual gazes at the target, the gaze direction of the individual exhibits successive gaze directions all over the place. very similar to the directions of gaze that this individual would have when reading a text.

The sequence of display positions successively taken by the visually dominant target is preferably predetermined as a function of a reference text, and / or a reading pattern, corresponding to the characteristics and / or read / write preferences of the user. the individual.

For example, the sequence can be predetermined beforehand with another device, during a calibration operation during which the individual is asked to choose a reference text, and / or a reading model, from among a number of plurality of real texts available and read it aloud. The reading speed can then be used as a parameter for determining the display positions of the target.

The sequence can also be predetermined as a function of the age of the individual or as a function of a reading level declared by the individual, following a questionnaire completed by the individual.

We can also consider doing a workout with a speed average, ask the individual if this average speed was too fast or not fast enough and adjust the speed according to their response.

We will first of all observe that the reading of a text by an individual is done naturally according to a reading scheme comprising three distinct operations: fixations, saccades and retro-saccades.

During fixations, the individual deciphers the word he is reading, that is to say the word on which the individual's gaze is fixed.

During saccades, corresponding to the phases of displacement, that is to say the passages from reading from one word to the next word, the eyes of the individual move rapidly to move from one fixation to another.

These saccades are linked to the visual span, that is to say to the number of characters (letters, symbols, ideograms, etc.) which are decipherable for a given fixation. They allow the reader to decipher all the characters of a text.

The saccades are generally made in the direction of the reading of the text. However, the eyes also perform very rapid “retro-saccades” in the direction opposite to the reading direction to switch from one fixation to another. This movement is induced by an error of the oculomotor muscles or by a bad reading and comprehension of the text.

One of the advantages of the test device 10 according to the invention is to provide visual monitoring protocols which come as close as possible to the reading patterns of the individual.

The test device 10 therefore makes it possible to simply simulate the reading of a text and to place the individual in a situation where he will adopt a natural posture close to that which he would adopt for reading in near vision.

A determination of the visual behavior of the individual under these conditions is therefore made more precise and the optical design of an ophthalmic lens intended for the individual can be improved so that the design of the ophthalmic lens meets the visual correction needs of the individual. 'individual.

Preferably, the positions of target 20 are aligned along at least two lines L1, L2 (case of positions 35, 36, 37, 38, 39 for line L2 of figure 3 ) substantially parallel. More precisely, in the exemplary embodiment shown in the figures, the control unit of the display 11 is programmed so that the successive display positions of the target 20 are aligned over five lines.

Alternatively, the positions of the target can be aligned in at least two columns.

In general, the positions of the target 20 can be aligned along parallel lines in any direction, in particular substantially horizontal or vertical for the individual 1.

More preferably, each row L1, L2, or alternatively each column, comprises at least three aligned positions of said target (case of positions 35, 36, 37, 38, 39 for row L2 of the figure 3 ).

In order for the visual tracking protocol to be the most representative of a reading by the wearer, provision is advantageously made for the visual tracking protocol to describe a reading path which conforms to that defined by a given writing system, so reproducing the movement of the gaze of the individual during reading in accordance with the writing system.

The reading path can be defined here as the path, at the level of the display 11, scanned by the gaze direction of the individual 1 when he looks at the sequence of positions 30 taken by the visually preponderant target 20.

The reading pattern adopted by an individual is linked not only to the nature or specific properties of the text, but also to the specifics of each writing.

It should also be noted that the different writings can be classified in a functional (alphabetic, syllabic or logographic writing) and directional (horizontal and vertical direction of writing and / or reading) manner.

Provision is therefore made in the test device for the control unit to memorize a vertical travel direction SV and a horizontal travel direction SH (see figure 3 ) privileged of the visual monitoring protocol.

This privileged direction of vertical and horizontal travel is determined beforehand according to the characteristics of the individual, and in particular his ability to read a text according to a given writing system.

For example, when the test device is used by a French person who reads from right to left and from top to bottom, the horizontal direction of travel memorized by the control unit is a direction of travel going from the left of the screen 11 to the right of screen 11, and the vertical travel direction memorized by the control unit is a travel direction going from the top of the screen 11 to the bottom of screen 11.

Also, in a preferred embodiment, the substantially parallel lines L1, L2 along which are aligned the positions 35, 36, 37, 38, 39 of the target 20 extend substantially horizontally, the direction of travel of the tracking protocol visual being identical for all the lines taken successively from the highest to the lowest, from left to right (or from right to left for a writing from right to left such as Arabic or Hebrew).

Likewise, when the test device is used by a Mongolian, who reads top to bottom and right to left, the vertical travel direction memorized by the control unit is a top travel direction. screen 11 at the bottom of screen 11, and the horizontal travel direction memorized by the control unit is a travel direction going from the right of the screen 11 to the left of the screen 11.

Also, in an embodiment suitable for this writing system, the substantially parallel lines along which the predetermined positions of the target are aligned extend substantially vertically, the direction of travel of the visual tracking protocol being identical, from above. down or from bottom to top, for all the lines taken successively from right to left.

Advantageously, the control unit of the test device 10 is programmed to allow the selection of the visual tracking protocol among a plurality of visual tracking protocols stored in a local or remote database, in which a direction of travel is. recorded in association with the visual monitoring protocol to which it corresponds.

Thus, the individual, depending on his own reading and / or writing characteristics, can choose the visual protocol which corresponds to him, so that he is in natural conditions close to reading when carrying out the visual test. We then make sure to set up our reading mechanisms and strategies in order to recover the posture that is most representative of the use of our near vision.

In order to reproduce the reading scheme as described above, with fixings, saccades and retro-saccades, provision is made for the control unit of the display 11 to display the target 20 according to a preferential visual monitoring protocol.

Also, it is expected that the control unit requires, in each position of the visual monitoring protocol, that the target 20 is displayed for a period of time. predetermined. This is understood to mean that the target 20 is kept displayed (case of position 34 of the figure 3 ) fixedly on the screen so that the individual 1 is forced to fix his gaze on the target 20, which corresponds to a fixation in the reading path of the individual 1.

Advantageously, the target is fixed during the predetermined time, that is to say that the position of the target 20 during this predetermined time does not change, before the passage to the next position of the reading path.

Preferably, this predetermined duration is between 50 milliseconds and 1 second, which typically corresponds to standard fixation times.

The predetermined duration may also vary during the reading journey, reflecting the fact that the fixing of the gaze of individual 1 on a word during an actual reading may depend on the word (size, length) and the level of reading. comprehension (poorly known or unknown word, poorly decipherable word or character, misspelled word, etc.).

Also advantageously, provision is made for the control unit to impose a predetermined delay between the displays of the target 20 in two successive positions 31, 32 (see figure 3 ) of the visual monitoring protocol.

In this way, thanks to the test device 10, it is possible to simulate the saccades or retro-saccades existing during the reading path of the individual 1. As previously, it is possible to provide for the control unit to vary the predetermined period during of the visual monitoring protocol.

This makes it possible to realize that the reading speed of the individual 1 can vary during the reading of a text.

This also makes it possible to consider the cases where the direction of gaze of the individual passes from one line to another, as is the case for example from position 51 to position 52 of the figure 3 , the return to the line requiring more time insofar as the variation in the direction of the individual's gaze is greater.

It is then possible to provide two cases for the target during the predetermined period.

In one embodiment, provision can be made for the target to be invisible for the predetermined period. This corresponds to the case of positions 31 and 32 of the figure 3 where the target 20 "jumps" (the jump being represented by the dotted arrow 40) from position 31 to the next position 32. This embodiment makes it possible to account for the gaze of the individual who jumps from word to word during reading a text.

In an alternative embodiment, provision can be made for the target to be visible for the predetermined period of time and to move between the two corresponding successive positions of the visual monitoring protocol, from one to the other. This corresponds to the case of positions 53 and 54 where the target moves (the movement being represented by the dotted arrow 49), while remaining visible (cf. targets 21, 22), from position 53 corresponding to the first position of the fourth line of the protocol at position 54 corresponding here to the second position of the fourth line of the protocol. This other embodiment, for its part, makes it possible to account for the gaze of the individual who browses the entire word before moving on to the next one when reading.

Advantageously, the test device 10 of the invention is such that the control unit requires that two successive positions 35, 36, 37, 38, 39 of the visual monitoring protocol are separated by a distance EM1, EM2, EM3, EM4 less than 10 centimeters. In this way, during the visual test, the individual 1 is not solicited so that the variation in his direction of gaze is not too great, which in reading condition is generally the case.

Preferably, provision is also made for the control unit to impose that the distance EM1, EM2, EM3, EM4 separating two successive positions 35, 36, 37, 38, 39 of the visual monitoring protocol varies along the visual monitoring protocol . This makes it possible to adapt the difference between the targets 20 displayed as a function of the average span of the words for a given writing system.

In another embodiment, the control unit is programmed so that the display of the target 20 in two successive positions of the visual tracking protocol follows the preferred direction of travel, horizontal and / or vertical, at least six times over. ten. This is illustrated on the figure 3 on which there is shown in the visual monitoring protocol, directions of travel, represented by the dotted arrows 43, 45, 48, which go not from left to right like the preferred direction of horizontal travel SH, but from right to left .

It is thus possible, thanks to this, to simulate the retro-saccade movements previously described during the reading of a text by individual 1. Indeed, here four times out of ten, the movement of the eyes 3 of the individual 1 following the target 20 of the gaze between two successive positions is done in the direction opposite to the preferred direction of travel.

As for the jerk movements detailed above, target 20 can move from one position to the next, in a direction of travel opposite to the preferred direction of travel, either by jumping from one position to another (invisible target ), or by moving from one to the other (visible target).

We will now describe, with reference to figures 4 to 18 , a method for determining at least one optical design parameter of an ophthalmic lens intended to equip a frame chosen by the individual, as a function of the visual behavior of the latter, this method using the test device described above. above.

1. a) on demande à l'individu d'effectuer une tâche visuelle dans laquelle il regarde la cible affichée par ledit afficheur du dispositif d'affichage, les positions de ladite cible étant prédéterminées dans un référentiel lié à un appareil de capture d'image,
2. b) on capture, au moyen dudit appareil de capture d'image, des images de la tête de l'individu regardant ladite cible, chaque image correspondant à une position prédéterminée de ladite cible,
3. c) on détermine, à partir d'une partie au moins des images de la tête de l'individu, des positions de la tête de l'individu dans un référentiel lié audit appareil de capture d'image ou des directions de regard de l'individu dans un référentiel lié à la tête de l'individu, chaque position de la tête ou direction de regard de l'individu étant associée à la position de ladite cible pour laquelle l'image correspondante de la tête de l'individu a été capturée,
4. d) on déduit ledit paramètre de conception optique recherché à partir desdites positions de tête ou direction de regard de l'individu.

According to the invention, the determination method comprises the following steps:

1. a) the individual is asked to perform a visual task in which he looks at the target displayed by said display of the display device, the positions of said target being predetermined in a frame of reference linked to an image capture device,
2. b) capturing, by means of said image capture device, images of the head of the individual looking at said target, each image corresponding to a predetermined position of said target,
3. c) determining, from at least part of the images of the individual's head, the positions of the individual's head in a frame of reference linked to said image capture device or the gaze directions of the individual. 'individual in a frame of reference linked to the head of the individual, each position of the head or direction of gaze of the individual being associated with the position of said target for which the corresponding image of the head of the individual has been captured,
4. d) said desired optical design parameter is deduced from said head positions or direction of gaze of the individual.

The figure 4 represents a logic diagram of different steps that can be implemented in an advantageous manner during the determination method of the invention. These different steps can be grouped into six blocks 100, 110, 120, 130, 140, and 150 comprising one or more sub-blocks each representing a particular step.

In practice, the tablet 10, or a local or remote computer, is programmed to perform the steps described below.

Block 100

In a prior identification step, represented by block 100 of the figure 4 , we ask the individual to fill in his name and surname. This step can be carried out using the tablet itself, for example by displaying on the screen 11 of the tablet 10 items to be completed by the individual 10.

During this identification step, the individual is also asked to select, according to his preferences or reading characteristics, an initial writing system by specifying the horizontal and vertical travel directions that should be favored: left right or right to left, and top to bottom or bottom to top.

Finally, a reading speed of the individual is memorized. This reading speed can be evaluated by asking the individual to indicate, for example by clicking on an icon displayed on the screen, whether his reading speed is slow, normal, or else fast. Depending on this reading speed, the predetermined duration of display of the target can be adjusted (see blocks 113 and 118 below).

As a variant, this reading speed could be evaluated on the basis of reading a real text, of sufficient length so that this reading speed corresponds to the average reading speed over the whole of the text read. Advantageously, the read text can be used to determine the display positions of the visually preponderant target of the visual monitoring protocol (cf. above).

We can also consider doing a workout with an average speed, asking the individual if this average speed was too fast or not fast enough and adjusting the speed according to his response.

All of this personal data can also be automatically retrieved from a database from the transmission to the database server of the name and first name of the individual and possibly other personal data such as age, address, etc ...

Block 110

The steps grouped together in block 110 of the figure 4 aim to build a frame of reference linked to the head 4 of the individual 1, called "LV posture frame of reference" or “CRO frame ”, in which the head 4 of the individual 1 has a fixed position and orientation and to which is associated a frame, preferably orthonormal, having an origin and three unrelated axes.

The figures 5 and 6 illustrate how this CRO benchmark is constructed.

In particular, the figure 5 a vertical plane PV corresponding to a sagittal plane of the head 4 of individual 1, which is the vertical plane passing through a perpendicular bisector of the two right and left eyes OD, OG of individual 1.

This perpendicular bisector of the eyes OD, OG is an axis which passes through the middle of a segment which is defined by the center of rotation of the right eye OD (hereinafter referred to as CROD) and the center of rotation of the left eye OG (hereinafter referenced CROG) and which is parallel to the Frankfurt plane of head 4 of individual 1.

The Frankfurt plane of the individual's head is defined as the plane passing through the lower orbital points of individual 1 and the porion of individual 1, the porion being the highest point of the skull in the ear canal, which corresponds to the tragion of the ear. For the determination of the Frankfurt plane, it is considered that the individual is in an orthostatic position, in which he performs a minimum of efforts. This position corresponds to a natural posture, hereinafter referred to as "VL posture".

In this natural position, the direction of gaze of the individual is then the primary direction of gaze, that is to say that he looks straight ahead. The Frankfurt plane is then generally horizontal.

We also define a horizontal plane PH which is, on the one hand, parallel to the Frankfurt plane of the head 4 of the individual 1 and, on the other hand, contains the centers of rotation CROD, CROG of the eyes OD, OG of the individual 1.

• une origine qui est l'un des centres de rotation CROD, CROG de l'œil droit OD ou de l'œil gauche OG de l'individu 1 ou un barycentre de ces centres de rotation CROD, CROG ;
• un premier axe qui passe par l'origine et les centres de rotation droit et gauche CROD, CROG,
• un deuxième axe qui passe par l'origine et qui est parallèle à la direction de regard primaire de l'individu 1, et
• un troisième axe qui passe par l'origine et qui est perpendiculaire aux premier et deuxième axe (le troisième axe correspond au « produit vectoriel » du deuxième axe avec le premier axe).

From the LV posture of individual 1, i.e. knowledge of the orientation of the Frankfurt plane, and the centers of rotation CROD, CROG of the eyes OD, OG of individual 1, it is possible to construct the reference CRO linked to the head 4 of the individual 1, hereinafter referenced R _CRO , by choosing:

• an origin which is one of the centers of rotation CROD, CROG of the right eye OD or of the left eye OG of individual 1 or a barycenter of these centers of rotation CROD, CROG;
• a first axis which passes through the origin and the right and left rotation centers CROD, CROG,
• a second axis which passes through the origin and which is parallel to the primary gaze direction of individual 1, and
• a third axis which passes through the origin and which is perpendicular to the first and second axis (the third axis corresponds to the “cross product” of the second axis with the first axis).

In the particular embodiment detailed here, the origin of the frame R _CRO is chosen as being the point located in the middle of the segment joining the center of rotation CROD of the right eye OD and the center of rotation CROG of the left eye OG of individual 1. In other words, this point of origin, hereinafter referred to as "CRO cyclops " and referenced CROc, corresponds to the isobarycenter of the centers of rotation CROD, CROG of the eyes OD, OG of the 'individual 1.

The three axes X _H , Y _H , Z _H , of the reference R _CRO are also represented on the figure 6 .

The X _H axis (first axis) is here oriented from the left center of rotation CROG to the right center of rotation CROD. The X _H axis is therefore contained in the horizontal plane PH parallel to the Frankfurt plane. An opposite orientation is also possible.

The Z _H axis (second axis) is located in the vertical plane PV of the head 4 of the individual 1 and is parallel to the Frankfurt plane. It is therefore parallel to the primary gaze direction when the individual 1 is in a natural position, that is to say in the LV posture. The axis Z _H extends here in a direction away from the head 4 of the individual 1 (towards the rear).

The axis Y _H (third axis) extends, for its part, in the vertical sagittal plane PV of the head 4 of the individual 1 and is perpendicular to the Frankfurt plane. The Y _H axis is therefore perpendicular to the X _H axis and to the Z _H axis. Here it is oriented upwards, so that the R _CRO mark is direct.

It will be noted that the reference R _CRO linked to the head 4 of the individual 1 and that therefore this reference R _CRO moves with the head 4 of the individual 1, the position and the orientation of this reference R _CRO changing with respect to an absolute or reference mark which would not be linked to the head 4 of the individual 1 according to the movements of the head 4 of the individual 1.

As mentioned above, the block 110 is intended to construct the reference R _CRO from the data supplied by the individual 1 or else from measurements taken on the individual 1.

Thus, in a step represented by sub-block 111, it is checked whether, for the individual 1 identified previously (see block 100), the positions of the centers of rotation CROD, CROG and the posture VL are available.

If these data are available, then we go to a step of creating the LV posture frame of reference as described above and represented by sub-block 112. The data can be available locally, that is to say recorded in a memory of the tablet 10, or else available remotely, that is to say recorded in a database on which requests can be made to retrieve said data.

If these data are not available, then it is necessary on the one hand to determine the respective positions of the centers of rotation CROD, CROG (sub-block 113) of the eyes OD, OG of individual 1, and on the other hand determine the VL posture (sub-block 114) of individual 1.

The determination of the positions of the CROD, CROG centers of rotation can be carried out according to the principle known per se and explained for example in the document FR 2914173 , of which an English equivalent is the document US 2010/0128220 .

During the step of determining the centers of rotation CROD, CROG (sub-block 113), the individual 1 wears, on his head 4, integral with the head 4, a marking system (metrological reference) or "clip" which comprises locating elements (markers) detectable during an image capture of the head 4 of the individual 1.

• une première image lorsque l'individu regarde l'appareil de capture d'images en se positionnant de face, en regardant au loin droit devant (posture VL), et
• une deuxième image lorsque l'individu regarde l'appareil de capture d'images en se positionnant de trois-quart.

In summary, at least two images of the head 4 of the individual 1 are captured by means of an image capture device:

• a first image when the individual looks at the image capture device while positioning himself in front, looking far straight ahead (VL posture), and
• a second image when the individual looks at the image capture device while positioning himself three-quarter.

If the tablet 10 is provided with a rear camera, the latter can advantageously serve as an image capture device. Otherwise, it is possible to provide an image capture device independent of the tablet.

From a processing of the two captured images (see document FR 2914173 ), one deduces the positions of the centers of rotation CROD, CROG in a repository linked to the tracking system.

It is then possible to determine a particular point, hereinafter designated “cyclops” or “cyclop CRO” center of rotation and referenced CRO _C , which is the isobarycenter of the two previously determined centers of rotation CROD, CROG.

In the next step of determining the LV posture, represented by sub-block 114, the positions of the centers of rotation CROD, CROG as well as the first image captured from the front are reused to determine the LV posture of the individual 1. Provision can also be made to compensate for the inclination of the shelf 10 during this last determination (see for example documents US 8231220 and US 7,950,800 ).

Thus, at the end of the steps represented by the sub-blocks 113 and 114, the data useful for the creation of the posture frame of reference VL are available and the creation step described above with reference to the sub-block 112 can be put. implemented.

Block 120

Then, in a set of steps represented by the block 120, adjustments are preferably made to the tablet 10 making it possible to improve the accuracy and reliability of the measurements of the position of the head 4 of the individual 1 or of the directions. view of the individual 1.

Thus, in a step represented by sub-block 121 and illustrated in figure 7 , the positions of the markers of the clip are determined in the field of the front camera 13 of the tablet 10, when the front camera 13 is oriented upwards.

For this purpose, an element is displayed in the center of the screen 11, here a circle 23, and the individual 1, who is holding the tablet 10 in hand, is asked to look at the circle 23.

As a variant, this element could be displayed at the first display position (see position 31 of the figure 3 ) of the target.

1. i) la position des marqueurs du clip est depuis un temps prédéfini dans les deux tiers supérieurs du champ de la caméra 13 ;
2. ii) la position des marqueurs du clip est depuis un temps défini dans le tiers inférieur du champ de la caméra 13 ; ou
3. iii) la position des marqueurs du clip est introuvable au delà d'un temps limite.

In a following step (sub-block 122), the front camera 13 of the tablet 10 is controlled to acquire images of the head 4 of the individual 1 equipped with the tracking system previously used and it is determined, from a processing of acquired images if:

1. i) the position of the clip's markers has been for a predefined time in the upper two thirds of the field of the camera 13;
2. ii) the position of the markers of the clip has been defined for a time in the lower third of the field of the camera 13; or
3. iii) the position of the clip's markers cannot be found beyond a time limit.

In case i), it is then possible to continue towards the step represented by the sub-block 131 of the training phase represented by the block 130.

In case iii) above, one continues to the step represented by the sub-block 123 during which a figure is displayed on the screen 11, here a cross 24 (see figure 8 ), indicating to individual 1 that a measurement error has been detected for the camera field 13.

Still in case iii) or in case ii), a figure is displayed on the screen 11, here an arrow 25 in the form of a circular arc (see figure 9 ), indicating to the individual 1 to turn the tablet 10 over so as to position the front camera 13 downwards.

Preferably, during this step, it is planned to verify that the tablet 10 has indeed been returned by the individual 1 (see figure 10 ). Advantageously, this verification can be carried out using orientation sensors of the tablet 10, for example of the gyrometer type.

Once the verification is done, we go to the step represented by the sub-block 124 and illustrated on the figure 11 , the positions of the markers of the clip are determined in the field of the front camera 13 of the tablet 10, when the front camera 13 is oriented downwards.

An element, here a circle 26, is then displayed in the center of the screen 11, and the individual 1, who is holding the tablet 10 in hand, is asked to look at this circle 26.

As a variant, this element could be displayed at the first display position (see position 31 of the figure 3 ) of the target.

In a next step (sub-block 125), the front camera 13 of the tablet 10 is controlled to acquire images of the head 4 of the individual 1 equipped with the tracking system previously used and holding the tablet in his hands 2.

1. i) la position des marqueurs du clip est depuis un temps prédéfini dans le champ de la caméra 13 ;
2. ii) la position des marqueurs du clip est introuvable au delà d'un temps limite.

It is then determined, from a processing of the images acquired, whether:

1. i) the position of the clip markers has been in the field of camera 13 for a predefined time;
2. ii) the position of the clip's markers cannot be found beyond a time limit.

In case i), it is then possible to continue towards the step represented by the sub-block 131 of the training phase represented by the block 130.

In case ii) above, one continues to the step represented by the sub-block 126 during which a symbol 27 is displayed on the screen 11 (see figure 11 ), signaling to individual 1 a non-detection of the clip or a calculation error.

Tablet 10 then displays a message and asks to restart the current step (see button 29) or to end the test (see button 28).

In addition, pictograms (not shown but which would be located in the blank boxes 99 of the figure 11 ) recalling the essentials of good practices are displayed.

• faire attention à la présence de lumières gênantes qui peuvent être source d'éblouissement (par ex. plafonniers, grandes baies vitrées dans le dos de l'individu) ;
• dégager le champ de vision de la caméra frontale 13 qui pourrait être obstrué par le doigt d'une main ou bien un vêtement qu'il porte.

For example, these pictograms can remind individual 1 to:

• pay attention to the presence of annoying lights that can be a source of glare (eg ceiling lights, large windows in the back of the individual);
• clear the field of view of the front camera 13 which could be obstructed by the finger of a hand or else a piece of clothing which it is wearing.

At the end of the steps of block 120 (adjustment phase), the front camera 13 of the tablet 10 was placed in the best conditions to take a measurement without the individual 1 readjusting his posture or the tablet 10 during the visual monitoring protocol.

Block 130

Preferably, steps 131, 132, 133, 134, 135 of block 130, which corresponds to a training phase, are performed before the actual measurement phase (steps of block 140, see figure 4 ).

In a first step of the training phase, either a memory is loaded into a memory provided for this purpose in the control unit, or a visual training monitoring protocol drawn at random from a set of visual monitoring protocols is calculated. accessible.

This set of accessible visual monitoring protocols is determined as a function of the privileged reading directions entered by the individual during the initialization step (block 100, see above). This set may be available directly in a memory of the tablet 10 or else downloaded from a remote server.

The visual monitoring protocol comprises data representative of the position of the visually preponderant target 20 to be displayed on the screen 11 of the tablet 10.

• un index (entier naturel) de la position de la cible 20 ;
• un repère temporel d'affichage de la cible 20 repéré et exprimé en secondes par rapport au début du protocole de suivi visuel ;
• deux coordonnées des positions d'affichage de la cible 20 sur l'écran 11, ces coordonnées étant exprimées par rapport à un repère d'écran, ci-après référencé R_SCR, ayant pour origine le coin supérieur gauche 90 de l'écran 11 (voir figure 12) et deux axes 91, 92 perpendiculaires entre eux et dirigés selon les colonnes et les lignes de l'écran 11.

These representative data include:

• an index (natural number) of the position of the target 20;
• a target display time mark 20 spotted and expressed in seconds with respect to the start of the visual monitoring protocol;
• two coordinates of the display positions of the target 20 on the screen 11, these coordinates being expressed with respect to a screen mark, hereinafter referenced R _SCR , originating from the upper left corner 90 of the screen 11 (see figure 12 ) and two axes 91, 92 perpendicular to each other and directed along the columns and rows of screen 11.

In other words, at each instant, the position of the target 20 is known in the screen mark R _SCR linked to the image capture device 13.

Once the visual monitoring protocol has been loaded, the target 20 is first displayed on the screen 11 of the tablet 10 in the first position (index = 0) of the visual monitoring protocol for a predefined time (sub-block 132 ). Provision can be made for an audible indicator or a vibration of the tablet 10 to indicate the start of the visual monitoring protocol.

Then (sub-block 133), the visually preponderant target 20 is displayed in its successive positions according to the chosen visual training monitoring protocol. The protocol run speed can be adjusted according to the information collected during the initialization phase (block 100) concerning the reading speed of individual 1.

During this step, the user 1 gets used to watching the visually preponderant target 20 sequentially taking all the predetermined display positions for the loaded visual training monitoring protocol.

As explained previously, the display positions of the target 20 are adapted to simulate the reading of a text by the individual 1. Thus, during the training phase (block 130), the user 1 will gradually adopt a posture corresponding to his natural posture in a pseudo-reading situation.

When the previous step (sub-block 133) is completed, it is preferably possible to display on screen 11 (see figure 13 , sub-block 134) a figure indicating the end of the cycle. An audible indicator or vibration may also indicate the end of the cycle.

At this step (sub-block 134), the displayed figure, here an arrow 81 directed upwards, represents an indicator encouraging the individual to look into the distance.

This figure 81 remains displayed on the screen 11 for a defined time before disappearing. The tablet 10 then displays nothing on the screen 11 and waits a defined time.

After this wait, the progress of the learning phase is checked (sub-block 135). In particular, if the user has only performed the visual monitoring protocol once, steps 133 and 134 are preferably repeated a second time. Otherwise, we go to the first step (sub-block 141) of the actual measurement phase (block 140).

Block 140

During this first step 141, which is similar to the first step 131 of the training phase (block 130), either a memory is loaded into a memory provided for this purpose in the control unit, or a monitoring protocol is calculated. visual measurement selected at random from the set of previously determined accessible visual monitoring protocols.

This visual monitoring protocol comprises similar data which is representative of the display position of the visually preponderant target 20 on the screen 11 of the tablet 10 during the measurement phase.

These data include in particular the display positions of the visually preponderant target 20 which are predetermined and known in the mark R _SCR linked to the image capture device (front camera 13) of the test device (tablet 10).

In a step a) of the method of determination according to the invention represented by the sub-blocks 142 and 143 of the figure 4 , the individual 1 is asked to perform a visual task in which he looks at the target 20 displayed by the screen 11 of the tablet 10 (see figure 16 ). The display positions 30 of this target 20 are predetermined in the reference R _SCR (cf. origin 90 and axes 91, 92 of the figure 3 ) linked to the front camera 13.

More precisely, we first display (sub-block 142), on screen 11 of the tablet 10, the target 20 in the first position 31 (index = 0) of the visual monitoring protocol loaded for the measurement for a predefined time.

Provision can also be made for an audible indicator or a vibration of the tablet 10 to indicate the start of the visual monitoring protocol.

Next (sub-block 143), the visually preponderant target 20 is displayed in its successive positions 30 according to the visual measurement monitoring protocol. The protocol run speed can be adjusted according to the information collected during the initialization phase (block 100) concerning the reading speed of individual 1.

During this step a), the user follows with his eyes the visually preponderant target 20 sequentially taking all of the display positions 30 predetermined for the loaded visual monitoring protocol (see figure 16 where target 20 is displayed at the last position of the visual tracking protocol).

During step b) of the determination method, represented by the sub-block 144, images of the front camera 13 of the tablet 10 facing the head 4 of the individual 1 are captured by means of the front camera 13 of the tablet 10 facing the head 4 of the individual 1. head 4 of individual 1 looking at target 20 which moves on screen 11 following the loaded visual monitoring protocol.

Advantageously, the front camera 13 triggers an image capture of the head 4 of the individual 1 with a capture offset with respect to the moment when the target 20 is displayed at the predetermined positions 20 of the visual monitoring protocol on the screen. 11. This offset may be zero, or else preferably small, for example less than 200 milliseconds. This makes it possible to take into account the reaction and movement time of the eyes 3 of the individual 1 during a change of position 30 of the target 20 on the screen 11.

According to a variant, the front camera can also produce a continuous video sequence, for example at a rate of twenty images per second, and extract from the video sequence the best image giving the best information on the visual behavior of the individual during target display at the corresponding target position.

Each image captured by the front camera 13 of the tablet 10 thus corresponds to a predetermined position of the visually preponderant target 20, whose position 30 in the R _SCR frame linked to the image capture device 13 is perfectly known (see sub-block 141 above and figure 16 ).

Then, in step c) of the determination method according to the invention, one determines, from at least part of the images of the head 4 of the individual 1, that is to say the positions of the head 4 of the 'individual 1 in the frame R _SCR linked to the front camera 13, or the gaze directions of the individual 1 in the frame R _CRO linked to the head 4 of the individual 1, each position of the head 4 or direction of gaze of the individual 1 being associated with the position 30 of the target 20 for which the corresponding image of the head 4 of the individual 1 has been captured.

To this end, there are provided image processing means of the tablet 10, constituted for example by the processor of the tablet 10, which detects in the images captured from the head 4 of the individual 1 the markers of the worn clip. by individual 1 on his head 4.

One then determines for each captured image, that is to say for each position 30 of the target 20 of the visual monitoring protocol, the position and the orientation of the clip in the frame R _SCR linked to the front camera 13 for example. using the process described in the document FR 2914173 (of which an English equivalent is the document US 8360580 ).

The positions of the centers of rotation CROD, CROG of the eyes of individual 1 with respect to the clip being known (see sub-blocks 111 and 114), the position (spatial coordinates) and orientation (angular coordinates) of the R _CRO reference frame linked to the head 4 of the individual 1 are also known from the clip.

This is also illustrated on the figure 16 where the reference R _CRO has been represented with its origin at the cyclopic center of rotation CRO _C (isobarycenter of the centers of rotation CROD, CROG) and its axes X _H , Y _H , Z _H.

Thus, by a change of frame, it is possible to determine, for each position 30 of the target 20 of the visual monitoring protocol, the position and the orientation of the head 4 of the individual 1 in the frame R _SCR linked to the front camera 13 of the tablet 10.

It is also possible to determine, for each position 30 of the target 20 of the visual monitoring protocol, the gaze directions DR of the individual 1 in the frame of reference R _CRO linked to the head 4 of the individual 1, these gaze directions DR joining here the cyclops center of rotation CRO _C , origin of the reference R _CRO linked to the head 4 of the individual 1, to the target 20.

You can also determine the viewing directions DRD, DRG (see figure 16 ) relating respectively to the right center of rotation CROD and to the left center of rotation CROG.

In a preferred embodiment, prior to step d), we then reexpress, from the positions and orientations of the head 4 or from the gaze directions DR of the individual 1, the positions 70 of the target 20 in the R _CRO mark linked to head 4 of individual 1.

This is illustrated on the figure 17 where there is shown with respect to the axes X _H , Y _H , Z _H of the frame R _CRO linked to the head 4 of the individual 1 the positions 70 of the target 20 in this frame R _CRO .

Given the fact not only that the position and orientation of the head 4 of the individual 1 changes during the visual test protocol with respect to the mark R _SCR linked to the image capture device 13 but also that the individual 1 modifies the position and the orientation of the tablet 10 during the visual test, it is understood that the relative positions 70 of the target 20 in the reference R _CRO linked to the head 4 of the individual 1 provide information on the visual behavior of the individual 1, in particular on his propensity to move his head 4 rather or rather his eyes 3 when reading a text.

Indeed, if the individual 1 follows the visual monitoring protocol, greatly modifying his gaze direction DR, then the relative positions 70 of the target 20 in the frame R _CRO linked to the head 4 of the individual 1 are similar to the positions 30 relative of the target 20 in the R _SCR frame linked to the front camera 13. This is the case of the figure 17 .

Conversely, if individual 1 follows the visual monitoring protocol while maintaining an almost fixed gaze direction DR, then the positions 70 of target 20 in the R _CRO frame linked to the head 4 of individual 1 are grouped together. This is the case with the figure 18 .

Furthermore, it is possible to associate these positions 70 of the target 20 in the frame R _CRO linked to the head 4 of the individual 1 with an index and a time frame as described above for the sub-block 141.

In a step d) of the determination method, represented here by sub-block 146, the desired optical design parameter is deduced from the head positions 4 or direction of gaze DR of the individual.

In the particular embodiment described, the desired optical design parameter is here deduced from the positions 70 of the target 20 in the R _CRO mark linked to head 4 of individual 1.

This optical design parameter can include, for example, the datum for the coordinates of the barycenter 71 of the positions 70 of the target 20 in the frame R _CRO linked to the head 4 of the individual 1. This barycenter 71 defines an average gaze direction of l 'individual 1 joining the cyclops center of rotation CRO _C and said barycenter 71.

This mean direction of gaze is representative of the visual behavior of individual 1 in near vision and in reading situation.

The data of the coordinates of the barycenter 71 in the frame R _CRO linked to the head 4 of the individual 1 can therefore be used to design an ophthalmic lens, in particular a progressive ophthalmic lens, intended to equip a spectacle frame chosen by the individual 1.

As described in the document FR 3012952 , it is for example possible, from the barycenter 71 and the mean gaze direction, to precisely position a reference point in near vision (VP centering point) on an ophthalmic lens and also to optimize the design of the surfaces front and back of the ophthalmic lens for a better adaptation of the latter to the individual 1.

Thanks to the positions 70 of the target 20 in the frame R _CRO linked to the head 4 of the individual 1, it is also possible to deduce an optical design parameter reflecting the tendency of the individual 1 to move the head 4 and / or eyes 3 during a reading task.

As mentioned above with reference to FIGS. 19 and 20, this optical design parameter can correspond to data representative of the dispersion of the positions 70 of the target 20 in the reference frame R _CRO linked to the head 4 of the individual 1.

This dispersion can be determined by calculating, for each position 70, the distance between this position 70 and the position of the barycenter 71 previously defined.

Since the positions 30 of the target 20 here extend horizontally and vertically, it is also possible to determine a horizontal dispersion coefficient and a vertical dispersion coefficient. The horizontal dispersion coefficient quantifies the movements of the eyes 3 of the individual 1 from left to right (or from right to left) during the visual monitoring protocol. The coefficient of vertical dispersion quantifies the movements of the eyes 3 of the individual 1 from top to bottom (or from bottom to top) during the visual monitoring protocol.

Other optical design parameters representative of the visual behavior of the individual can of course be determined.

In a following step, represented here by sub-block 147, it is verified that the determination of the optical design parameter has been carried out successfully.

For example, when this optical design parameter includes the data of the coordinates of the barycenter 71 (see figure 17 ) of the positions 70 of the target in the frame linked to the head 4 of the individual 1, it is possible to verify that the coordinates of this barycenter 71 are included in specific ranges which are a function of the positions 30 of the target 20 in the frame R _SCR of the tablet and the minimum and / or maximum range of motion of the head 4 of individual 1.

• si c'est la première fois que la mesure est faite alors l'erreur est maintenue et un signal d'erreur (ici une croix 83, voir figure 15) est affiché sur l'écran 11 de la tablette 10 (sous-bloc 148, voir aussi sous-bloc 126) ;
• si c'est la deuxième mesure et si une erreur est signalée alors l'erreur est annulée et toutes les valeurs sont figées à la limite minimale. Ce cas sera détecté comme une valeur aberrante et sera géré en conséquence.

Any value determined outside these limits generates an error. Two cases are then possible:

• if it is the first time that the measurement is made then the error is maintained and an error signal (here a cross 83, see figure 15 ) is displayed on screen 11 of tablet 10 (sub-block 148, see also sub-block 126);
• if this is the second measurement and if an error is signaled then the error is canceled and all values are frozen at the minimum limit. This case will be detected as an outlier and will be handled accordingly.

If the previous check goes well, a success symbol is displayed on the screen (see symbol 82 in the form of V on the figure 14 ) and one passes to the next step which is represented by the sub-block 149 and which consists in encoding the various optical design parameters deduced in a determined format.

It is for example possible to encode each of the coordinates of the barycenter 71 of the positions 70 of the target 20 in the frame R _CRO linked to the head 4 of the individual 1 in a hexadecimal base, on one or more bytes, preferably two bytes.

Block 150

During a transfer phase (block 150), the optical design parameters are transmitted to a local or remote computer intended to use said parameters with a view to the optical design of an ophthalmic lens intended for the individual 1 and particularly well suited to his visual behavior, here his reading behavior in near vision.

Claims (14)

1. Device (10) for testing the visual behavior of an individual (1), this device including:

   - an active display (11) suitable for displaying at least one visually predominant target (20) in a plurality of positions (30) that vary over time and that are aligned in at least one row (L1, L2) or one column, and

   - a unit for controlling the display (11), this unit being programmed so that the successively displayed positions (30) of the target (20) follow, over time, a visual tracking protocol
   characterized in that:

   all the successively displayed positions (30) are such that the target (20) is in the visual field of the individual, and

   the visually predominant target (20) is a target that is suitable for catching the eye of said individual (1) following said target (20) during the eye test, said visual tracking protocol corresponding to the succession, over time, of positions adopted by the visually predominant target (20), said target (20) imposing a visual tracking protocol on the individual (1) who successively looks in a plurality of particular desired directions that are each associated with a particular display position (30) adopted by the target (20) .
2. Testing device (10) according to Claim 1, wherein said positions (30) of the target (20) are aligned in at least two rows (L1, L2) or two columns that are substantially parallel.
3. Testing device (10) according to either of Claims 1 and 2, wherein said plurality comprises, in each row or column, at least three aligned positions (35, 36, 37) of said target (20).
4. Testing device (10) according to one of Claims 1 to 3, wherein the controlling unit makes it so that, in each position (30) of said visual tracking protocol, the target (20) is displayed for a predetermined duration.
5. Testing device (10) according to Claim 4, wherein said predetermined duration is comprised between 50 milliseconds and 1 second.
6. Testing device (10) according to Claim 4 or 5, wherein said target (20) remains stationary for said predetermined duration.
7. Testing device (10) according to one of Claims 1 to 6, wherein the controlling unit makes it so that there is a predetermined lag between the display of the target (20) in two successive positions (30) of the visual tracking protocol.
8. Testing device (10) according to Claim 7, wherein said predetermined lag varies over the course of the visual tracking protocol.
9. Testing device (10) according to one of Claims 1 to 8, wherein said controlling unit makes it so that two successive positions (30) of the visual tracking protocol are separated by a distance (EM1, EM2, EM3, EM4) smaller than 10 centimeters.
10. Testing device (10) according to one of Claims 1 to 9, wherein said controlling unit makes it so that two successive positions (30) of the visual tracking protocol are separated by a distance (EM1, EM2, EM3, EM4) that varies throughout the visual tracking protocol.
11. Testing device (10) according to one of Claims 1 to 10, wherein said controlling unit stores a favored vertical direction of travel (SV) and a favored horizontal direction of travel (SH) of the visual tracking protocol in memory.
12. Testing device (10) according to one of Claims 1 to 11, wherein the visual tracking protocol follows a reading trajectory which accords with that defined by a given writing system, so as to reproduce the displacement of the gaze of the individual (1) while reading in accordance with the writing system.
13. Method for determining at least one optical parameter for designing an ophthalmic lens intended to be mounted in a frame chosen by the individual (1), depending on the visual behavior of the latter, said method using the testing device (10) according to one of Claims 1 to 12 and comprising the following steps:

    a) the individual (1) is asked to perform a visual task in which they look at the visually predominant target (20) that is displayed by said display (11) of the display device and that is suitable for catching the eye of said individual (1) during the eye test, said target (20) imposing a visual tracking protocol on the individual (1) who successively looks in a plurality of particular desired directions that are each associated with a particular display position (30) adopted by the target (20), said visual tracking protocol corresponding to the succession, over time, of positions adopted by the visually predominant target (20), the positions (30) of said target (20) being predetermined in a frame of reference attached to an image-capturing apparatus,

    b) images of the head of the individual (1) looking at said target (20) are captured by means of said image-capturing apparatus, each image corresponding to a predetermined position (30) of said target (20),

    c) on the basis of at least some of the images of the head of the individual (1), positions of the head of the individual (1) in a frame of reference attached to said image-capturing apparatus or gaze directions (DR) of the individual (1) in a frame of reference attached to the head of the individual (1) are determined, each position of the head or gaze direction of the individual (1) being associated with the position (30) of said target (20) for which the corresponding image of the head of the individual (1) was captured,

    d) said sought-after optical design parameter is deduced from said positions of the head or gaze direction of the individual (1).
14. Determining method according to Claim 13, wherein, prior to step d), the positions (70) of said target (20) are re-expressed, on the basis of said determined positions of the head or the gaze directions of the individual (1), in a frame of reference attached to the head of the individual (1), and, in step d), said sought-after optical design parameter is deduced from said positions (70) of the target (20) in the frame of reference attached to the head of the individual (1).

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